For an optical system used with electronic imaging apparatus like digital cameras and digital video cameras, it is now required to have small-format size and optical performance high enough to be well corrected for aberrations. As one approach to achieving size reduction, there has been a bending or flexion optical system known in the art that includes a reflective optical element inside as well as an electronic imaging apparatus incorporating the same.
For the bending optical systems including a reflective optical element, a small-format imaging optical system of positive-negative-positive-positive-negative-positive six-groups construction has been known as set forth in the following patent publications.
JP(A)'s 2009-69671, 2009-192771, 2008-225314 and 2008-129238 have proposed a high-zoom-ratio bending optical system of the positive-negative-positive-positive-negative-positive six-groups construction wherein the second, the fourth and the fifth lens groups are used as zooming groups and the fourth and/or the fifth lens group are used as focusing lens groups.